This project is involved with the development of a radioimmunoassay for endogenous human renin circulating in the blood stream. Currently methods for assay of human renin depend on "effective renin activity" and the end stage product angiotensin determined either biologically in a rat assay or with an immunoassay for angiotensin II. Renin is an enzyme manufactured by the kidney which acts on a substrate, an alpha globulin to form angiotensin I, then angiotensin II. In order to study the entire system, the actual quantitation of renin will be necessary. This involves several facets that we have already completed: (1) Purification of human renin- Renin has been purified to a high degree although proof of purity has not been established as of this writing. Four basic extraction steps are used with ammonium sulfate and acetone precipitation described by previous investigators. These purification steps are augmented by acetylated DEAE chromatography followed by isoelectric focusing column and polyacrylamide gel electrophoresis. (2) Radioactive renin - Renin has been labeled, although specific activity for radioactivity is not as high as desired for the renin immunoassay. The labeling has been done with I-131 that is most effective, done by the method of Hunter and Greenwood. (3) Radioimmunoassay - An immunoassay system has been standardized using the double antibody precipitation method for separating bound and free renin. A variation of this assay has been with sephadex coated with antibody. This is easily precipitable and slightly easier technically than the double antibody. After the radio immunoassay has been perfected, it will be used to screen population for renin abnormalities that are associated with pathological disease states such as toxemia of pregnancy, renal hypertension, essential hypertension, and hyperaldosteronism.